Solid gas generating units



some GAS GENERATING UNITS Alexander Cantlay Hutcllison, Saltcoats,Scotland, assignor to Imperial Chemical Industries Limited, acorporation of Great Britain No Drawing. Application April 8, H54,Serial No. 421,981

4 Claims. (Cl. 52-0.5)

The present invention is concerned with improvements in solid gasgenerating units comprising solid gas generating charges of the kindcapable of propagating through themselves a self-sustained, exothermic,non-detonating, gas-evolving decomposition when a merely local portionof the charge is heated from room temperature to the temperature atwhich its active decomposition begins or which in combination with oneor more components of said units are capable of decomposing in saidmanner. Solid gas generating charges of the kind capable of propagatingthrough themselves a self-sustained, exothermic, non-detonating,gas-evolving decomposition in the aforesaid manner have foundapplication for a variety of purposes including, for instance, theactuation of gas pressure operated mechanical devices, blastingoperations, the

dispersion of volatilisable pesticides, insect repellents,

rodenticides, propulsion of rockets, the expulsion of liquids fromcontainers such as fire extinguishers and the driving of turbines.

This application is a continuation-in-part of my application, Serial No.123,981 filed October 27, 1949.

It is known that guanidine nitrate undergoes an exothcrmic gas evolvingdecomposition but only when it is strongly heated. Under atmosphericpressure conditions the reaction does not sustain itself if a portiononly of a quantity or" the compound is heated from atmospherictemperature to the temperature at which decomposition begins, unlessexternal heating is maintained. The decomposition leads to theproduction of gases containing steam, nitrogen, ammonia and oxides ofcarbon, but there is also formed a certain amount of a difiicultlyfusible yellow nitrogenous organic residue.

Conversely, when the conditions are such that the prevailing gaspressure is sufiiciently high, namely of the order of 70 atmospheres,once the reaction has been locally initiated it will sustain itselfthroughout a mass of the guanidine nitrate.

Attempts have been made to provide charges capable of decomposing with ahigh yield of permanent gases when locally heated by a non-detonatingelement, at a lower pressure than guanidine nitrate, said mixtures comprising guanidine nitrate with a proportion of a metallic hypophosphiteor ammonium hypophosphite whereby, if desired, charges capable ofsupporting their decompositions even at atmospheric pressure whenlocally heated may be obtained. I

However, owing to the nature or amount of the residue the hypophosphitesleave behind or other disadvantages attendant on their employment thesecharges have only a limited applicability and it would be desirable toprovide improved gas generating charges based on guanidine nitrateand/or nitroguanidine, and capable of self-sustained decomposition underconditions of much lower gas pressure than guanidine nitrate alone.

it is also known that the pressure required to render possible theself-sustained decomposition of a charge based on guanidine nitrate maybe progressively reduced by making up the guanidine nitrate into chargeswith progres- "nited States atent ice sively increasing amounts ofcolloided nitrocellulose as a binding agent, by mixing the guanidinenitrate with a solution of nitrocellulose in a volatile solvent, formingthe resulting paste into the required shape and evaporating oil thevolatile solvent, but the use of a volatile solvent adds to the expenseand necessitates a drying operation, while the applicability of thismethod is also somewhat limited.

Prior art in the field show gas producing charges comprisingnitroguanidine and/or guanidine nitrate and a pulverulent metal,non-metal, or metallic compound sensitiser, other than a metallichypophosphite or ammonium hypophosphite, for the thermal decompositionof nitroguanidine and/ or guanidine nitrate.

Further, such art shows that gas-generating charges suitable for avariety of purposes, free from disadvanrages attendant on the use ofhypophosphite or gelatinised nitrocellulose and capable ofself-sustained nondetonating decomposition when merely locally heated,providing a high yield of hot gases and maintaining propagation of thereaction under considerably lower gas pressures than are required forguanidine nitrate, may be obtained by the use in admixture withguanidine nitrate of a polynitro-phenol or a polynitroso-phenol. Gasgenerating charges are disclosed comprising guanidine nitrate inadmixture with a polynitro-phenol or a polynitroso-phenol. These chargesmay include if desired an aliphatic carboxylic acid selected from thegroup consisting of tartaric, maleic, citric and fumaric acids with orwithout the inclusion of a small proportion of vanadium pentoxide whichif desired may be in the form of a chemically equivalent vanadiumcompound. These charges may also include a small percentage of a heatresisting material having a large surface area and amounting to not lessthan 0.25% of the weight of the charge.

The principal object of the present invention is to provide gasgenerating units adapted to generate hot gases at temperatures higherthan 600 C., said gas generating units comprising nitroguanidine and/orguanidine nitrate, at least one non-explosive inorganic reagent which insufficient amount is able to eiiect a self-sustained thermaldecomposition of nitroguanidine and/ or guanidine nitrate when locallyheated and a heat-resisting material having a large surface area.

Another object of this invention is to provide gas generating units asnoted heretofore wherein said inorganic reagent is selected from thegroup consisting of molybdic acid, ceric oxide, and vandaium pentoxideand said heat resisting material is asbestos fibre.

A further object of this invention is to provide gas generating units asnoted heretofore wherein said nitrogen containing compound is in amountof from about 89% to 98.8% by weight of the total unit, said inorganicreagent is in amount of from about 0.2% to 10% by weight of the totalunit, i. e., the ratio by weight of the nitrogen containing compound tothe inorganic reagent is between the values of 98.8 to 0.2 and 89 to 10,and the heat resisting material is in amount of from about 0.25% to 1%by weight of the total unit.

The heat resisting material having a large surface area is alwaysmaintained in immediate proximity to an exposed surface ofnitroguanidine and/or guanidine nitrate composition undergoing thermaldecomposition at said surface. Thus, the condensable vapourisableorganic compounds that are formed are caused to pass, before coolingtakes place, over or through said heat resisting material therebycausing a further exothermic reaction and so further increasing thetemperature and the yield of hot gases. The heat resisting material mayeither be external to the nitroguanidine and/or guanidine nitratecomposition, or may be actually included in the composition. If the heatresisting material is external to the composition, then, of course, anyamount thereof can be used governed only by economy and convenience.However, if the heat resisting material is actually included in thecomposition, then an amount of from about 0.25% to 1% by weight of thetotal unit is contemplated. A preferred range for the heat resistingmaterial wien included in the composition is from about 0.25% to 0.5% byweight of the total unit.

Examples of the said non-explosive inorganic reagents which insufficient amount either alone or in conjunction one with another areable to effect the self-sustained thermal decomposition ofnitroguanidine and/or guanidine nitrate when locally heated are molybdicacid, eerie oxide, and vanadium pentoxide. As noted heretofore, suchnon-explosive inorganic reagent must be in amount of from about 0.2% to10% by weight of the total unit. A preferred range for the inorganicreagent is from about 0.2% to 6% by weight of the total unit.

The said non-explosive inorganic reagents need not be incorporated inthe nitroguanidine and/or guanidine nitrate but may be included in thesaid heat resisting material which although maintained in immediateproximity to the one or more surfaces of the nitroguanidine and/orguanidine nitrate which are to undergo selfsu'stained thermaldecomposition is nevertheless wholly external to such surface orsurfaces.

The non-explosive inorganic reagent utilized in this invention is suchthat, in the absence of said heat resisting material having a largesurface area, it is unable to bring about the desired completeself-sustained thermal decomposition.

As noted heretofore, the nitrogen containing compound can be in amountof 89% to 98.8% by weight of the total unit.

Gas generating units made in accordance with the invention may be used,for instance, for actuating gas pressure operated mechanical devices, e.g. for driving engines and turbines, or for operating pneumatic tools,for operating fire extinguishers, for propulsion of rockets or other gasescape reaction propelled devices, e. g. jet

propelled toys and models, for inflation of buoyant apparatus, clearingobstructed pipes, for making colored smokes or for safety blastingoperations by means of blasting assemblies in which the charge of thegas generating unit is caused to undergo decomposition in a pressureresisting container adapted to vent the gas once a predeterminedpressure has been built up within the container.

It will be understood that according to the purpose for which the gasgenerating unit is required the charge of said unit may be in powder,granular or compact form of any required shape.

The preferred ranges noted heretofore for the basic ingredients of thegas generating unit are illustrated by the following examples in whichthe parts are parts by weight.

EXAMPLE 1 A mixture consisting of the following ingredients:

Parts Guanidine nitrate 94.7

Molybdic acid 5.0 Asbestos fibre 0.3

is prepared by grinding the ingredients in a pestle and mortar until anintimate mixture is obtained. 45 gms. of the mixture is then loaded intoa 1" diameter cartridge tube rolled from absestos paper and isconsolidated by pressing, the cartridge being supported for the timebeing by a steel mould. The pressed cartridge is placed in a steelvessel of 100 cu. ins. capacity, the vessel closed and the chargeignited electrically. The charge decomposes in a self-sustained mannergiving oif a steady stream of gas over a period of 2%. minutes therebyraising the pressure in the vessel to 260 lbs./ sq. in. The hot broadaspect.

gases are evolved at a temperature of between 900 C. to 1000 C., but arerapidly cooled by loss of heat to the walls of the vessel. The pressurefalls slightly to 230 lbs/sq. in. as temperature equilibrium is reached.This experiment shows the suitability of the composition for the slowgeneration of gas pressure for such uses as the expulsion of liquidsfrom fire extinguishers or the inflation of buoyant apparatus or thelike.

EXAMPLE 2 Instead of using molybdic acid as sensitising agent forguanidine nitrate as quoted in Example 1, ceric oxide is used in thefollowing proportion:

Parts Guanidine nitrate 94.5 Ceric oxide 5.0 Asbestos fibre 0.5

The above composition may be compressed into solid charges of anydesired shape and used for such requirements as are indicated in Example1.

The temperature of the hot gases evolved is about 900 C. to 1000 C.

EXAMPLE 3 Instead of using eerie oxide, vanadium pentoxide is employedas a sensitising agent for the guanidine nitrate as in the followingcomposition.

Parts Guanidine nitrate 98.5 Vanadium pentoxide 1.0 Asbestos fibre 0.5

The temperature of the hot gases evolved is about 900 C. to 1000 C.

EXAMPLE 4 A porous pad of asbestos fibre is arranged to be maintained inclose contact with the surfaces of a compressed charge of any of thecompositions mentioned in Examples l to 3 which are, however, to be freefrom asbestos fibre. Then if surfaces of the charge adjacent to theporous pad of asbestos fibre are heated e. g. by an incendiary mixture,to cause partial decomposition and volatilization of the guanidinenitrate mixture a gas phase reaction takes place in the asbestos fibreof said porous pad and liberates sufficient heat to decompose moreguanidine nitrate mixture and so on. A self-sustained decomposition ofthe mixture is thereby obtained provided that the asbestos pad is keptadjacent to the reacting surface or the charge. A gas generating unitconstructed in this way forms a convenient means for obtaining aselfsustained gas producing reaction having a particularly advantageousfeature in that the charge of said unit may be one which reacts only onthe surface adjacent to the asbestos pad. This makes it possible toobtain a controlled burning of a charge in one direction only withoutelaborate protection of side surfaces.

The temperature of the hot gases evolved is about 900 C. to 1000 C.

The following examples set out in tabular form are also submitted sincethey illustrate the invention in its These examples show use of thevarious ingredients in the broad ranges noted heretofore and parts areparts by weight.

The charges are constructed so that the diameter of each cartridge is1.5 inches, so that the weight of the composition in each cartridge is70 gms. and so that the composition is directly pressed in an asbestoslining positioned in a cylindrical steel vessel 3.5 inches deep and 1.5inches diameter in which vessel the cartridge thus formed is fired undera pressure of the order of 400 1b./ sq. in. in an atmosphere ofnitrogen.

Components:

Guanidine nitrate Components:

Nitroguanidine 98. 8 98. 8 98. 8 89 89 89 98. 5 98. 5 98. 5 Asbestos 1.0 1. 0 1.0 1.0 1. 0 1. Q 0. 25 0. 25 0. 25 Molybdic aoid 0.2 10. 0 1. 25Oeric oxide 0. 2 10. 0 1. 25 Vanadium pentoxi e.- 0. 2 10.0 1. 25 Lengthof charge (ins) 1. 82 1. 67 2.15 1. 71 1.78 1. 76 1. 79 1. 77 1. 86 Timeof burning (sees 27. 0 26. 25 31. 75 17. 0 26. 0 10. 25 47. 9 22. 2 14.5 Pressure (p. s. i.)... 500 450 400 500 43 450 500 500 460 Burningspeed (ins. .068 .064 .068 106 .069 172 .037 .080 13 I claim:

1. A gas generating unit capable of propagating throughout itself aself-sustained exothermic non-detonating gas evolving decompositioncomprising in association at least one nitrogen containing compoundselected from the group consisting of nitroguanidine and guanidinenitrate, at least one non-explosive inorganic reagent selected from thegroup consisting of molybdic acid, ceric oxide, and vanadium pentoxide,and a heat resisting material consisting of asbestos fibre wherein theratio by weight of the nitrogen containing compound to the inorganicreagent is between the values of 98.8 to 0.2 and 89 to 10.

2. A gas generating unit capable of propagating throughout itself aself-sustained exothermic non-detonating gas evolving decompositioncomprising in association at least one nitrogen containing compoundselected from the group consisting of nitroguanidine and guanidinenitrate in amount of from about 98.8% to 89% by Weight of the totalunit, at least one non-explosive inorganic reagent selected from thegroup consisting of molybdic acid, ceric oxide, and vanadium pentoxidein amount of from about 0.2% to 10% by weight of the total unit, and aheat resisting material consisting of asbestos fibre wherein said heatresisting material is in admixture with the nitrogen containing compoundand the non-explosive inorganic reagent and is in amount of from about0.25% to 1% by weight of the total unit.

3. A gas generating unit as claimed in claim 1 wherein said heatresisting material is maintained in the immediate proximity of at leastone exposed surface of the composition comprising said nitrogencontaining compound.

4. A gas generating unit as claimed in claim 1 wherein said nitrogencontaining compound is guanidine nitrate.

No references cited.

1. A GAS GENERATING UNIT CAPABLE OF PROPAGATING THROUGHOUT ITSELF ASELF-SUBSTAINED EXOTHERMIC NON-DECONATING GAS EVOLVING DECOMPOSITIONCOMPRISING IN ASSOCIATION AT LEAST ONE NITROGEN CONTAINING COMPOUNDSELECTED FROM THE GROUP CONSISTING OF NITROGUANIDINE AND GUANIDINENITRATE, AT LEAST ONE NON-EXPLOSIVE INORGANIC REAGENT SELECTED FROM THEGROUP CONSISTING OF MOLYBDIC ACID, CERIC OXIDE, AND VANADIUM PENTOXIDE,AND A HEAT RESISTING MATERIAL CONSISTING OF ASBESTOS FIBRE WHEREIN THERATIO BY WEIGHT OF THE NITROGEN CONTAINING COMPOUND TO THE INORGANICREAGENT IS BETWEEN THE VALUES OF 98.8 TO 0.2 AND 89 TO 10.